This paper presents a modified skyhook-inertance control strategy which is realized through a hydraulic device of continuously adjustable inertance between sprung mass and unsprung mass. The parasitic damping inherent in the hydraulic device as well as the inertance is taken into account in the modified control strategy. Differential equation models are built to compare the performance of the semiactive suspension employing the modified control strategy with that of the passive suspension. The results demonstrate that the semiactive suspension significantly reduces sprung mass natural frequency, attenuates the resonant peak value without the penalty of deterioration at higher frequencies, and achieves over 28% improvement on ride comfort, compared with the passive suspension in unload condition. The proposed hydraulic device, together with its control strategy, can be used to reduce the variation of sprung mass natural frequency and ride comfort between unload and full-load condition.
A new two-terminal mechanical element named the mem-inerter described by a relation between integrated momentum and displacement is introduced as the memory counterpart of an inerter. It exhibits an individual ''fingermark'' featured by a pinched hysteresis loop located within the momentum-velocity plane. The mem-inerter is attached to a simple mass-spring-damper system. The system equipped with a mem-inerter is mathematically modeled, and its nonlinear vibration equation is derived. To ensure a fair performance comparison between the systems equipped with the meminerter and the inerter, the nonlinear mem-inerter with an appropriate helix pitch can be proved to be equivalent to the linear inerter with a fixed inertance by the fact that the systems have the same displacement transmissibility for forced response. Under such a premise, it is found that the system with the mem-inerter having positive initial displacement has better performance for free response than the system with the inerter. Furthermore, the application scenario that both systems are arranged on an inclined plane is taken as an example of the positive initial displacement. The example demonstrates that the system with the mem-inerter has significantly better transient performance than the system with the inerter.
In order to design a comfortable-oriented vehicle suspension structure, the network synthesis method was utilized to transfer the problem into solving a timing robust control problem and determine the structure of ''inerter-spring-damper'' suspension. Bilinear Matrix Inequality was utilized to obtain the timing transfer function. Then, the transfer function of suspension system can be physically implemented by passive elements such as spring, damper, and inerter. By analyzing the sensitivity and quantum genetic algorithm, the optimized parameters of inerter-spring-damper suspension were determined. A quarter-car model was established. The performance of the inerter-spring-damper suspension was verified under random input. The simulation results manifested that the dynamic performance of the proposed suspension was enhanced in contrast with traditional suspension. The root mean square of vehicle body acceleration decreases by 18.9%. The inerter-spring-damper suspension can inhibit the vertical vibration within the frequency of 1-3 Hz effectively and enhance the performance of ride comfort significantly.
To realize the control of the inerter and establish a more realistic model of the controllable inerter, this paper designs a controllable inerter and analyzes its nonlinear factors. The ideal model, conventional nonlinear model, and calibrated nonlinear model of the controllable inerter are analyzed and the compressibility of fluid is studied. The prototype of a controllable inerter is tested on the bench and the friction force is identified. The bulk modulus of the fluid in controllable inerter in the fluid-air mixture condition and the pure fluid condition are analyzed. A suspension kinetics model with nonlinear controllable inerter is established. And the performances of the suspension with different nonlinear models are analyzed. The result shows that the inerter force can be reflected through the calibrated nonlinear model. The mixed air has a serious negative effect on the suspension performance and the nonlinear factors will take a negative effect on the control results.
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